Fullerene-containing optical materials with novel light transmission characteristics

ABSTRACT

Optical glasses and polymers are described that incorporate homogeneously dispersed fullerene molecules. The resultant materials may be used as optical filters, the cut-off frequency being easily adjustable by changing the fullerene content. To prepare glasses fullerene molecules are firstly functionalized by amination prior to being incorporated into a sol-gel process to prepare the glass. To prepare polymers a pre-existing polymer may be subject to fullerenation, or fullerene may be copolymerized with a selected monomer.

FIELD OF THE INVENTION

This invention relates to optical materials suitable for use as filters,and in particular to such materials incorporating fullerenes.

BACKGROUND OF THE INVENTION

Optical materials with filtering characteristics have many applications.One of the most obvious is to provide protection against the harmfuleffects of sunlight. The effects of excessive sunlight on the human bodyand eye are well known, and in addition exposure to strong sunlight cancause milk to degrade, beer to deteriorate and oil to become rancid.Over-exposure to sunlight is one of the major causes of opthalmicdamage, including the formation of cataracts and tissue injury in theretina. Exposure of the body to sunlight can cause sunburn, erythema,skin cancer and premature ageing.

It is known that the damaging effect of light is wavelength dependant.Short wavelength (<400 nm) radiation induces photodegradation of manyfoods and beverages. Excessive exposure of the body to ultraviolet (UV)light promotes severe deterioration of the epidermis. UV light is alsoinjurious to the eye, and strong blue and green light in the 400-550 nmrange is harmful to visual performance. Light with a wavelength longerthan 600 nm is generally harmless but can, under certain circumstancescause damage due to its thermal heating effect on the receptor segmentsin the retinal cells.

Another driving force for developing optical filter materials comes fromtechnological development. Many modern technologies are based onphotosensitive materials, for example photoresists for fabrication ofintegrated-circuit computer chips, photocurable polymer-dispersed liquidcrystals for display systems, and colour films for photoimagingprocesses. Many pharmaceutical and medical products such as drugs,photocurable dental bonding resins, and polymer-based controlled drugdelivery devices undergo undesirable photodegradation during storage. Inaddition many people such as welders, smelters, semi-conductor cleanroom operators, computer operators and laser operators need to beprotected from prolonged exposure to strong and/or constant lightemission.

PRIOR ART

Traditionally glass coloured with metal ions has been used to filter orcut off unwanted light. Although glass has been produced for thousandsof years, the conventional technology for producing coloured cut-offglass consumes a tremendous amount of energy in a high-temperatureprocess. The process is complex, involving batching, melting and formingsteps in which a large amount (30-50 wt %) of many--normally 5 to9--different kinds of components (eg metal oxides) have to be mixed withsilica at high temperatures (several hundreds to thousands of degrees)with subsequent involved thermal post-treatments. Changing the cut-offwavelength of such a glass is not a trivial task: the components andtheir ratios and all the processing conditions must be carefullychanged.

Because plastic offers various advantages, including low cost, lowdensity, high flexibility, and high impact strength, it is rapidlyreplacing glass in many applications. The most commonly used methods forproducing light-filtering plastics are the hot- or cold-dip dyeingprocesses in which the optical plastics are immersed in the hot or colddye solution for some time to allow the dye to penetrate into theplastic matrix. The dyeing is a physical blending process, however, andthus the dye content and distribution in the plastics may change withtime when in use, thus causing problems in stability and reliability intheir wavelength-blocking performance. In addition changing the cut-offwavelengths of optical plastics is not easy: different dyes and theircombinations must be used, which sometimes results in the formation ofvery dark plastics.

The optical properties of fullerene containing materials have recentlybegun to be explored. For example fullerene containing materials areknown to have optical limiting properties (see for example U.S. Pat. No.5,172,278). Difficulties arise, however, when attempts are made toincorporate fullerene into glasses and optical plastics. Simple physicalblending leads to inhomogeneous compositions due to phase separationproblems while previous attempts to incorporate the fullerene at amolecular level have resulted in the fullerene structure being damaged.

SUMMARY OF THE INVENTION

According to the present invention there is provided an opticalfiltering material comprising fullerene molecules homogeneouslydispersed within said material. The cut-off frequency of the filteringmaterial may be easily selected by adjusting the fullerene content. Thematerial may be a glass, a polymer material, a solution, a lotion, acream or other forms.

In this specification the term "fullerene" means not only C₆₀(buckminster-fullerene) but also the higher molecular weight fullerenes(C₇₀, C₈₄ . . . ) and also their derivatives.

In a first embodiment of the invention the material is a glass and saidfullerene molecules are firstly functionalised by reaction before beingincorporated into said glass in a sol-gel process. By functionalisingthe C₆₀ the fullerene may be made soluble in a solvent suitable forsol-gel processing (eg ethanol/water) thus enabling fullerene to behomogeneously dispersed in the resulting glass avoiding the problems ofinhomogeneity that may occur when fullerene is incorporated by a simpleprocess of physical blending. The reaction may be amination,hydroxylation, alkylation, or cycloaddition.

When the reaction is an amination reaction it may comprise reacting C₆₀with an amine derivative such as a primary, secondary or tertiaryamines, for example 6-amino-1-hexanol, cyclohexylamine,2-(2-aminoethoxy)ethanol, ethanolaime or 3-aminopropyltriethoxysilane.In the subsequent sol-gel reaction a solution of the C₆₀ -aminederivative (eg in ethanol) is reacted with a metal alkoxide such astetraethylorthosilicate (TEOS). The speed of the gel formation may becontrolled by the addition of a suitable drying-control chemicaladditive such as 2-hydroxyethyl methacrylate, propyltrimethoxysilane,3-(trimethylsilyl)propyl methacrylate, glycerol, DMF, DMSO, or any othersuitable high boiling point or viscous liquid.

In other embodiments the material is a polymer such as polycarbonate,poly(vinyl chloride), polystyrene, CR-39, poly(methyl methacrylate),poly(hydroxyethyl methacrylate), polyethylene, polypropylene,poly(norbornylene), polyalkynes, poly(dimethylsiloxane), poly(ethyleneteraphthalate), nylons, polyurethanes, or their copolymers or mixtures.A number of different techniques may be employed including:acid-catalysed, photolysis-induced, and radical-initiated fullerenationof existing polymers; thermally induced copolymerisation; andpreparation of a physically blended mix of polymer and C₆₀ followed bythermally induced fullerenation of the polymer.

The invention also extends to methods of manufacturing optical filteringmaterials. In particular the invention extends to a method ofmanufacturing an optical filtering glass comprising, functionalising C₆₀by reaction and adding said functionalised C₆₀ to a sol-gel reactionprocess. The invention also extends to a method of manufacturing anoptical filtering polymer comprising the step of fullerenation of apolymer to create a copolymer having fullerene chemically incorporatedtherein. The invention further extends to a method for the manufactureof an optical filter polymer comprising the copolymerisation of C₆₀ witha selected monomer.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention will now be described by way ofexample and with reference to the accompanying Figures, in which:

FIGS. 1(a)-(c) show the UV absorption spectra for certain sol-gelglasses prepared in accordance with embodiments of the invention,

FIGS. 2(a)-(c) show the UV absorption spectra for certain opticalpolymers prepared in accordance with embodiments of this invention,

FIGS. 3(a)-(d) show the UV spectra for still further optical polymersprepared in accordance with embodiments of this invention,

FIG. 4 is an ¹ H NMR spectrum of a C₆₀ -amine derivative,

FIGS. 5(a) and (b) are respectively linear and semilogarithmic plots ofthe transmission spectra of ethanol solutions of H_(x) C₆₀ [NH(CH₂)₆OH]_(x),

FIG. 6 is a plot showing the effect of concentration of the C₆₀ -aminederivative in FIGS. 5(a) and (b) on the cut-off wavelengths in differentsolvents,

FIGS. 7(a) and (b) are respectively transmission spectra of ethanolsolutions of H_(x) C₆₀ [NH(CH₂)₃ Si(OEt)₃ ]_(x) and H_(x) C₆₀(NH-cyclo-C₆ H₁₁)_(x),

FIG. 8 shows the concentration dependence of the cut-off wavelength invarious H_(x) C₆₀ (NHR)_(x) solutions,

FIG. 9 shows the stability of the cut-off frequency over time,

FIG. 10 shows the transmission spectra of poly(C₆₀ -co-MMA),

FIGS. 11(a) and (b) show respectively the concentration dependence ofthe cut-off frequency in poly(C₆₀ -co-MMA) and poly(C₆₀ -co-styrene),

FIGS. 12(a)-(c) show respectively the concentration dependence of thecut-off frequency in C₆₀ -containing polycarbonates prepared by (a)AIBN-induced, (b) UV-induced, and (c) AlCl₃ -catalyzed fullerenations,

FIG. 13 shows the concentration dependence of the cut-off frequency inC₆₀ -containing poly(vinyl chloride)s prepared by AIBN-inducedfullerenation,

FIG. 14 shows the transmission spectra of C₆₀ -CR-39 copolymer films,

FIG. 15 shows the concentration and pathlength dependence of cut-offwavelength of C₆₀ -CR-39 and C₆₀ -styrene copolymer films,

FIG. 16 shows the concentration and pathlength dependence of the cut-offwavelength of H_(x) C₆₀ [NH(CH₂)₃ SiO_(3/2) ]-SiO₂ sol-gel glassesprepared with various drying-control chemical additives, and

FIGS. 17(a) and (b) show respectively the concentration dependence ofthe cut-off wavelength of H_(x) C₆₀ [NH(CH₂)₆ OH]_(x) /SiO₂ and H_(x)C₆₀ (NH-cyclo-C₆ H₁₁)_(x) /SiO₂ sol-gel glasses prepared with or withoutdrying-control chemical additives.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In a first embodiment fullerenes may be incorporated into inorganicglasses by firstly functionalising the fullerenes by means of anamination reaction, followed by chemically incorporating the fullerenesinto the glass by means of sol-gel processing.

Different C₆₀ -amine derivatives were prepared using similar generalprocedures. The reaction was:

    C.sub.60 +NHRR'→H.sub.x C.sub.60 (NRR').sub.x

The fullerene and the amine compounds reacted in bulk under nitrogen at100° C. for 24 hours. At the beginning fullerene particles weresuspended in the amine compound but they gradually dissolved to formclear brown solution when the reaction proceeded. By checking usingthin-layer chromatography using hexane as eluent, no unreacted fullerenewas detected. The crude product was pre-treated to remove part of theunreacted amine compound. To further remove the amine compound the crudeproduct was purified by either running silica-gel column orprecipitation. The details for the synthesis of some C₆₀ -aminederivatives are shown as follows:

EXAMPLE 1 Synthesis of H_(x) C₆₀ [NH(CH₂)₆ OH]_(x) (1a)

A 25 ml flask was charged with 104 mg of C₆₀ and 2 g of6-amino-1-hexanol. The content was gradually warmed to 100° C. andstirred for 24 hours under a dry nitrogen atmosphere. To remove theunreacted 6-amino-1-hexanol, the crude product was dissolved in a smallamount (10 ml) of methanol which was then added dropwise into a largeamount (500 ml) of acetonitrile under continuous stirring. Theprecipitate was filtered off by a Gooch crucible, washed withacetonitrile, and dried at room temperature. The isolated product wasdissolved in methanol again, and further purified through a silica-gelcolumn using methanol as an eluent. Brown powder (yield: 183 mg) wasobtained.

EXAMPLE 2 Synthesis of H_(x) C₆₀ [NH-cyclo-C₆ H₁₁ ]_(x) (1b)

A 25 ml flask was charged with 50 mg of C₆₀ and 2 ml of cyclohexylamine.After the reaction, part of the unreacted amine compound was removed byprecipitating into acetonitrile. The crude product was purified byrunning silica gel column using methanol as eluent. Dark brown powder(yield: 78 mg) was obtained.

EXAMPLE 3 Synthesis of H_(x) C₆₀ [NH(CH₂ CH₂ O)₂ H]_(x) (1c)

108 mg of C₆₀ and 2 ml of 2-(2-aminoethoxy)ethanol were added into a 25ml flask. Again the mixture was heated at 100° C. under nitrogen for 24hours. Purification of the product was achieved by precipitating into ca400 ml of ethyl acetate. The precipitated product was filtered off usinga Gooch crucible and dried at room temperature under vacuum. Dark brownpowder (yield: 210 mg) was obtained.

EXAMPLE 4 Synthesis of H_(x) C₆₀ [NH(CH₂)₃ Si(OEt)₃ ]_(x) (1d)

A 25 ml flask was charged with 108 mg of C₆₀ and 5 ml of3-aminopropyltriethoxysilane. After the reaction proceeded for 24 hoursthe unreacted amine compound was distilled off from the reaction mixtureunder vacuum. Purification of the product was achieved by a silica-gelcolumn using ethanol as an eluent. Dark brown solid (yield: 78 mg) wasobtained.

The chemical structure and composition of the C₆₀ -amine derivatives maybe fully characterized by spectroscopic analysis. FIG. 4 shows the ¹ HNMR spectrum of H_(x) C₆₀ [NH(CH₂)₆ OH]_(x). The addition of the aminecompounds into fullerene is supported by the observation of a broad peakat δ(1H) 4.110 ppm which refers to C--H fullerene skeletal hydrogens.The ¹ H NMR spectra for other H_(x) C₆₀ (NHR)_(x) also have this broadpeak which confirms the structure of the C₆₀ -amine derivatives seeTable 1.

                  TABLE 1                                                         ______________________________________                                        .sup.1 H NMR Data for H.sub.x C.sub.60 (NHR).sub.x                            ______________________________________                                         ##STR1##                  (1a).sup.b                                          ##STR2##                  (1b).sup.c                                          ##STR3##                  (1c).sup.b                                          ##STR4##                  (1d).sup.d                                         ______________________________________                                         .sup.a Chemical shifts relative to TMS (ppm).                                 .sup.b In chloroformd/DMSO-d.sub.6.                                           .sup.c In chloroformd.                                                        .sup.d In DMSOd.sub.6.                                                   

The aminated fullerene derivatives obtained by Examples 1 to 4 above maybe incorporated into glasses using a sol-gel process. Sol-gel processingis an attractive possibility for incorporating fullerene into a glassmainly due to the relatively low temperature at which a glass can beprepared. The sol-gel process, in general, involves three steps: (i)conversion of metal alkoxides to gels through hydrolysis andpolycondensation reactions; (ii) drying of gels (gelation); and (iii)transformation of gels to glasses under elevated temperatures withoutmelting. In the first step, the change of metal alkoxides to polymericspecies through hydrolysis and condensation is as follows:

hydrolysis

    .tbd.Si--OR+H.sub.2 O→.tbd.Si--OH+ROH

condensation

    .tbd.Si--OR+HO--Si.tbd.→.tbd.Si--O--Si+ROH.tbd.Si--OH+HO--Si.tbd..fwdarw..tbd.Si--O--Si.tbd.+H.sub.2 O

In order to control the hydrolysis reaction an acid or base such as HClor NH₄ OH is often employed as a catalyst. With HCl transparent highdensity dry gels consisting of small particles (<20 Å) are obtained,whereas with NH₄ OH opaline and low density dry gels are made. Severalfurther factors, eg the concentration of the catalyst, the mole ratiobetween water and metal alkoxides, the nature of alkoxy groups on thesilicon atom and the solvent, temperature etc. will all influence thegel structure.

It is also important to minimize drying stresses to avoid cracking inthe glass during drying, and it is important to control pore sizedistributions and the rate of evaporation of the pore liquor which arefactors leading to drying stresses. This can cause it to take a verylong time to complete the drying step and produce a crack free glass.The addition of drying control chemical additives (DCCA) can alleviatethis problem. DCCAs can reduce the gelation, ageing, drying times anddrying stress, and can assist in the production of larger sizemonoliths.

Since the major components in a common sol-gel reaction system aretetraethylorthosilicate (TEOS), ethanol and water, the aminationreaction makes C₆₀ TEOS-compatible and EtOH/H₂ O-soluble so that ahomogeneous and transparent glass can be obtained. The general processmay be considered to be as follows. The sol-gel reaction is performed ina 25 ml 2-necked flask. Drying-control chemical additives (DCCA), either2-hydroxyethyl methacrylate (HEMA), propyltrimethoxysilane (PTMS) or3-(trimethylsilyl)propyl methacrylate (TMSPMA) may be added to controlthe gel formation. The mixture is heated at 60° C. for 1 hour undernitrogen. Part of the solvent is distilled off using an evaporator at50° C. and the concentrated viscous sol solution was poured into a Petridish which was then covered with parafilm. After two days a hole is madein the parafilm with a syringe needle to allow evaporation of thevolatiles and the evaporation rate may be controlled by opening one morehole in the parafilm every three days. After the dish has been stored atroom temperature for about 2 months a sol-gel glass is obtained.

Sol-gel glasses with different C₆₀ contents are prepared by changing thefeed ratios of the derivative to tetraethyl orthosilicate (TEOS) in thesol-gel reaction mixture. The following examples describe thepreparation of C₆₀ (for comparison) and C₆₀ -amine derivative containingsol-gel glasses.

EXAMPLE 5 Preparation of Sol-gel Glasses with C₆₀

The reaction is as follows: ##STR5##

1. 5 ml of TEOS and 1 ml of toluene were added into a degassed 25 mltwo-necked flask. A pre-mixed solution consisting of 1.3 ml of water,1.4 ml of ethanol, 1.5 ml of hydrochloric acid (HCl) (0.48M), and 2.5 mlof 0.01% toluene solution of C₆₀ were transferred to the flask at roomtemperature. The mixture was then stirred at 60° C. under nitrogen forone hour. Allowing the solvent to evaporate gradually a paleyellow-coloured C₆₀ --SiO₂ glass with big black particles was obtainedafter three months.

2. A drying control chemical additive such as 2-hydroxyethylmethacrylate (HEMA) may also be used.

2.8 mg of 2,2'-azobis(2-methylpropionitrile), (AIBN) was added into a 25ml two-necked flask. The system was degassed by nitrogen for threetimes. Then 5 ml of TEOS and 0.15 ml of 2-hydroxyethyl methacrylate(HEMA) was added. A pre-mixed solution consisting of 1.3 ml of water,1.4 ml of ethanol, 1.5 ml of HCl (0.48M), and 1 ml of 0.01% toluenesolution of C₆₀ were transferred to the flask at room temperature. Themixture was then stirred at 60° C. under nitrogen for 1 hour. Allowingthe solvent to evaporate gradually a pale yellow coloured C₆₀ --SiO₂with small black particles (thickness: 1.75 mm) was obtained after twomonths.

3. An alternative DCCA such as propyltrimethoxysilane (PTMS) may also beused.

A 25 ml two-necked flask was degassed by nitrogen three times. 7 ml ofTEOS, 0.28 ml of PTMS and 1 ml of toluene were added. A pre-mixedsolution consisting of 1.7 ml of water, 1.9 ml of ethanol, 2 ml of HCl(0.48M), 1 ml of 0.01% toluene solution of C₆₀, and 1 drop of glycerolwere transferred to the flask at room temperature. The mixture was thenstirred at 60° C. under nitrogen for 1 hour. By carefully controllingthe solvent evaporation rate, a pale yellow-coloured C₆₀ --SiO₂ withsmall black particles (thickness: 1.75 mm) was obtained after twomonths.

EXAMPLE 6 Preparation of Sol-gel Glasses (2a) Containing (1a)

The reaction is as follows: ##STR6##

1. The sol-gel glass was prepared using the same procedure as in Example5.1 except that a premixed solution consisting of 1.3 ml of water, 1.4ml of ethanol, 1.5 ml of HCl (0.48M) and 0.3 ml of ethanol solution of1a (11.456 mg/ml) were added. In addition no toluene was used. Atransparent brown-coloured monolith 2a with a thickness of 1.78 mm wasobtained after two months.

2. Using HEMA as DCCA a sol-gel glass was prepared using the sameprocedure as in Example 5.2 except that a pre-mixed solution consistingof 1.3 ml of water, 1.4 ml of ethanol, 1.5 ml of HCl (0.48M), and 0.2 mlof ethanol solution of 1a (11.456 mg/ml) were added. In addition notoluene was used. A transparent brown-coloured monolith 2a with athickness of 1.79 mm was obtained after two months.

3. Using TMSPMA as DCCA 6 mg of AIBN was added into a 25 ml two-neckedflask. The system was degassed by nitrogen three times. 5 ml of TEOS and0.2 ml of 3-(trimethylsilyl)propyl methacrylate (TMSPMA) were added. Apremixed solution consisting of 1 ml of water, 1.4 ml of ethanol, 1.5 mlof HCl (0.48M), and 0.3 ml of ethanol solution of 1a (3.104 mg/ml) weretransferred to the flask. The mixture was then stirred at 60° C. undernitrogen for one hour. Carefully controlling the solvent evaporationyielded a transparent brown-coloured monolith 2a with a thickness of1.85 mm after two months.

EXAMPLE 7 Preparation of Sol-gel Glasses (2b) Containing (1b)

The reaction is as follows: ##STR7##

The preparation procedures were the same as in Example 5.1 except forthe addition of 0.3 ml of ethanol solution of 1b instead of 0.01%toluene solution of C₆₀. Besides that, no toluene was added. Atransparent brown-coloured monolith 2b with a thickness of 1.42 mm wasobtained after two months.

EXAMPLE 8 Preparation of Sol-gel Glasses (2d) Containing (1d)

The reaction is: ##STR8##

1. The sol-gel glass was prepared using the same procedures as inExample 5.2 except that 0.1 ml of ethanol solution of 1d (11.8 mg/ml)was added instead of 0.01% toluene solution of C₆₀. Also no toluene wasadded. A transparent brown-coloured monolith 2d with a thickness of 1.64mm was obtained after two months.

2. The sol-gel glass was prepared using the same procedure as in Example5.3 except for the addition of 0.05 ml of ethanol solution of 1d (11.8mg/ml) instead of 0.01% toluene solution of C₆₀. Also no toluene wasadded. A transparent brown-coloured monolith 2d with a thickness of 1.81mm was obtained after two months.

Analysis of the sol-gel glasses produced by Examples 5 to 8 revealedthat for the C₆₀ /SiO₂ glasses numerous aggregated fullerene clusterswere suspended within the SiO₂ matrix, even for very low fullerenecontent (ca 0.0097%). On the other hand sol-gel glasses prepared withaminated fullerene derivatives were homogeneous and transparent. Noaggregated clusters or separated "islands" were observed in theseglasses, although their fullerene contents (ca 0.55%) were much higher.

FIGS. 1(a)-(c) show the UV spectra (recorded using a Milton RoySpectronic 3000 Array Spectrometer) for sol-gel glasses 2a, 2b, 2drespectively. For comparison the UV spectra of C₆₀ (thin solid line) and"pure" C₆₀ -containing sol-gel glasses (dotted line--Example 5.2 forFIG. 1(a) & (c), Example 5.3 for FIG. 1(b)) are also shown. FIGS.1(a)-(c) show that the absorption spectra of sol-gel glasses containingaminated fullerenes are completely structureless in comparison to freefullerene. In addition the absorption spectra are red-shifted relativeto that of pure fullerene containing sol-gel glasses. The degree ofred-shift is dependent on the fullerene content (a greater red-shift forgreater fullerene content) which means that the cut-off frequency can becontrolled by appropriate selection of the fullerene content.Furthermore the fullerene-derivative containing glasses werehomogeneous, thermally stable, optically transparent and crack free. Themonoliths obtained were all with a diameter of 28-30 mm and a thicknessof 1.22 to 2.01 mm.

The above Examples illustrate the preparation of glasses incorporatingfunctionalised fullerenes to provide glasses having desirable opticalproperties. However, given the increasing use of optical plastics thecreation of fullerene containing optical plastics materials with similarproperties would clearly be desirable.

EXAMPLE 9 Acid-catalyzed Fullerenation of Polycarbonate

A baked 50 ml two-necked pear-shaped flask was charged with 508.2 mg ofpolycarbonate (PC) and 5 mg of C₆₀. Then 15 ml of1,1,2,2-tetrachloroethane (CHCl₂ CHCl₂) was added. After PC and C₆₀completely dissolved the whole system was degassed three times bynitrogen. PC/C₆₀ solution was transferred into a saturated solution ofaluminium chloride (AlCl₃) under room temperature and then the mixturewas heated at 140° C. under nitrogen. After ca. 30 minutes the purplesolution gradually changed to a brown solution. After 24 hours a littleamount of polymer solution was precipitated in 5 ml of hexane. Thehexane solution was filtered through cotton wool. Evaporating thefiltrate solution, redissolving particles (if any) in 1 ml of toluene,and checking the toluene solution by UV measurement indicating thatthere is no unreacted C₆₀ left. Then the reaction was quenched by theaddition of a few drops of water. The whole reaction mixture wastransferred to a separation funnel and washed with 15 ml of water forthree times to remove residual catalyst AlCl₃. The organic layer wascollected, dried over anhydrous sodium sulphate and evaporated to yielda brown solid. The brown solid redissolved in ca. 20 ml of THF and thesolution was added dropwise through cotton wool to 1 liter of hexane.The precipitated polymer was filtered off using a Gooch crucible anddried at room temperature under vacuum for 2 days. Brown solid (yield:97.2%) was obtained. C₆₀ -PC polymers with other C₆₀ contents wereprepared similarly by changing the initial feed ratios.

EXAMPLE 10 UV-induced Fullerenation of Polycarbonate

500.6 mg of polycarbonate (PC), 10.8 mg of C₆₀ and 10 ml CHCl₂ CHCl₂were added into a round-bottomed flask. After all PC and C₆₀ particleswere completely dissolved, 7 ml solution mixture was transferred to aquartz tube and was degassed by nitrogen three times. The solutionmixture with continuous stirring was irradiated with 200 W Hg lamp undernitrogen. The progress of the reaction was checked continuously by asimilar method to the one set out in Example 9. After 35 hours it wasfound that there was no unreacted C₆₀ and the whole reaction mixture wasadded dropwise through cotton wool to ca. 1 liter hexane. Theprecipitated copolymer was filtered off using a Gooch crucible and driedat room temperature under vacuum for 2 days. Brown solid (yield: 92.6%)was obtained. C₆₀ -PC polymers with other C₆₀ contents may be preparedby appropriately changing the feed ratios.

EXAMPLE 11 AIBN-initiated Fullerenation of Polycarbonate

A 25 ml round-bottomed flask was charged with 506 mg of polycarbonate(PC) and 5 mg of C₆₀. Then 10 ml of CHCl₂ CHCl₂ was added to the flask.After the PC and C₆₀ had completely dissolved, 5.6 mg of2,2'-azobisisobutyronitrile (AIBN) was added and then the whole reactionmixture was degassed by nitrogen for three times. Stirring at 60° C.under nitrogen for about one hour changed the solution from purple tobrown in colour. After 24 hours similar methods to those described inthe previous examples were employed to establish that no C₆₀ wasunreacted. Then the reaction mixture was added dropwise through cottonwool to 1 liter hexane. The precipitated crude product was filtered offusing a Gooch crucible and dried at room temperature under vacuum forone day. Brown solid was redissolved in ca. 10 ml of THF and the brownsolution was precipitated through cotton wool to about 1 liter ofmethanol under stirring. Repeated precipitation of polymer in hexane andmethanol was done until the C₆₀ -AIBN adducts were removed which wasindicated by a GPC (gel-permeation chromatography) chromatogram. Theprecipitated polymer was filtered off using a Gooch crucible and driedat room temperature under vacuum for two days. Brown solid (yield:94.0%) was obtained. C₆₀ -PC polymers with other C₆₀ contents can beprepared in similar manner by changing the initial feed ratio.

EXAMPLE 12 AIBN-initiated Fullerenation of Poly(vinyl Chloride)

A 25 ml round-bottomed flask was charged with 506 mg ofpoly(vinylchloride) (PVC) and 5 mg of C₆₀. Then 18 ml of chlorobenzenewas added to the flask. After the PVC and C₆₀ completely dissolved, 22.8mg of AIBN was added. The reaction mixture was stirred at 60° C. undernitrogen for 24 hours and the crude product was obtained. Aftersubsequent purification as described in the previous Example brown solid(yield: 83.9%) was obtained. C₆₀ -PVC polymers with other C₆₀ contentscan be obtained by changing the initial feed ratio.

EXAMPLE 13 Preparation of C₆₀ -CR-39 Copolymer Films

0.6 mg of C₆₀ and 82.6 mg of AIBN were added into a 25 ml two-neckedround-bottomed flask. The whole system was degassed by nitrogen threetimes. Then 4 ml of di(ethylene glycol)bis(allyl carbonate) (CR-39) wasadded and the reaction mixture heated at 60° C. under nitrogen. C₆₀particles were gradually dissolved to form a clear pale brown solution.After 12 hours a similar method to those previously described was usedto confirm that no unreacted C₆₀ remained. Then the whole productsolution was filtered through cotton wool. No particles were left on thecotton wool indicating that no insoluble polymers were formed during thepolymerisation. Pouring the polymer solution onto a glass plate, heatingat 60° C. for 2 hours and 80° C. for 24 hours yielded a pale brownmembrane with a thickness of 455 μm. C₆₀ -CR-39 crosslinked copolymerswith other C₆₀ contents can be made by changing the initial feed ratios.

EXAMPLE 14 Copolymerisation of C₆₀ with Methyl Methacrylate

16.4 mg of C₆₀, 46.3 mg of AIBN, and 4.8 ml of methyl methacrylate (MMA)were added into a baked 25 mm round-bottomed flask. Stirring thereaction mixture at 70° C. under nitrogen for 24 hours yielded a browncrude product. After purification and filtering using the previouslydescribed techniques brown solid (yield:53.7%) was obtained. C₆₀ -MMAcopolymers with other C₆₀ contents can be manufactured by changing theinitial feed ratios.

EXAMPLE 15 Copolymerisation of C₆₀ with Styrene

20 mg of CO₆₀, 25 mg of 2,2'-azobisisobutyronitrle (AIBN), and 4.8 ml ofstyrene were added into a baked 25 ml round-bottomed flask. After thereaction and then subsequent purification as previously described, abrown solid (yield:55.7%) was obtained. C₆₀ -styrene copolymers withother C₆₀ contents can be manufactured by changing the initial feedratios.

FIGS. 2(a)-(c) and FIGS. 3(a)-(d) illustrate the UV spectra of variousC₆₀ containing polymers.

In FIGS. 2(a)-(c) each figure shows the spectra of (1) C₆₀, (2)polycarbonate (PC), and (3) C₆₀ -containing PC prepared by fullerenationinduced by AlCl₃ catalyst (FIG. 2(a)), UV irradiation (FIG. 2(b)), andAIBN initiation (FIG. 2(c)). The C₆₀ content (wt %) was 2.28% (FIG.2(a)), 5.76% (FIG. 2(b)), and 6.30% (FIG. 2(c)). The concentration(mg/ml) of C₆₀ in FIGS. 2(a)-(c) was 0.011; concentration of PC/THF inFIGS. 2(a)-(c) was 0.475; and the concentration of C₆₀ -PC/THF was 0.25(FIG. 2(a)), 0.3 (FIG. 2(b)), and 0.275 (FIG. 2(c)).

FIG. 3(a) compares UV absorption spectra for (1) C₆₀ (0.11 mg/ml C₆₀/hexane), (2) PVC (23.375 mg/ml PVC/THF), and (3) C₆₀ -PVC (0.4 mg/mlC₆₀ -PVC/THF, C₆₀ content 4.98 wt %).

FIG. 3(b) compares UV absorption spectra for (1) C₆₀ (as for FIG. 3(a)),(2) CR-39 (455 μm film thickness) and (3) C₆₀ -CR-39 (82 μm filmthickness, C₆₀ content 0.22 wt %).

FIG. 3(c) compares UV spectra for (1) C₆₀ (as for FIG. 3(a)), (2) PS(0.45 mg/ml PS/THF), and (3) C₆₀ -PS (0.45 mg/ml C₆₀ -PS/THF, C₆₀content 1.14 wt %).

FIG. 3(d) compares UV spectra for (1) C₆₀ (as for FIG. 3(a)), (2) PMMA(4.075 mg/ml PMMA/THF) and (3) C₆₀ -PMMA (0.85 mg/ml C₆₀ -PMMA/THF, C₆₀content 0.97 wt %).

These figures show that the absorption spectra in the visible region ofthe C₆₀ containing polymers are very different from both the free C₆₀and the parent polymers. The characteristic absorption band of fullereneat 329 nm disappears and is replaced by a steadily decreasing absorbancecurve toward a longer wavelength without any pronounced maxima whichappears to be the tail of an intense absorption band in the UV region.

In addition to the above examples C₆₀ -containing PMMA, PS, PC and PVCmay be made by a process of thermal-induced fullerenation. In each casethe process is very similar. Apart from PVC, a polymer membrane wasobtained with physical blending of C₆₀ by adding polymer, C₆₀ andsolvent to a 50 ml round-bottomed flask. After the polymer and C₆₀ weredissolved the solution was poured into a Petri dish. Allowing a slowrate of evaporation at room temperature yielded a polymer membrane withphysically blended C₆₀.

The membrane was then further dried at room temperature under vacuum forone day and then cut into small pieces and transferred to a schlenk. Themembrane is heated to about the temperature at which the polymer meltsand after the reaction the resulting polymer is dissolved in THF and thesolution precipitated dropwise through cotton wool into 1 liter hexane.The precipitated polymer was filtered off using a Gooch crucible anddried at room temperature under vacuum for 2 days.

EXAMPLE 16 Preparation of C₆₀ -PMMA Polymer

518.2 mg of PMMA, 5.2 mg of C₆₀ and 10 ml toluene were used to preparethe C₆₀ /PMMA membrane. Heating at 190° C. for 1 hour under nitrogenyielded brown solid. After precipitation and drying a dark brown fibre(yield: 88%) was obtained.

EXAMPLE 17 Preparation of C₆₀ -PS Polymer

615 mg of PS, 6.2 mg of C₆₀ and 10 ml of toluene were used to preparethe C₆₀ /PS membrane. Heating at 190° C. for 1 hour under nitrogenyielded brown solid. After precipitation and drying, a dark brown fibre(yield: 97%) was obtained.

EXAMPLE 18 Preparation of C₆₀ -PC polymer

555.7 mg of PC, 5.5 mg of C₆₀ and 10 ml CHCl₂ CHCl₂ were used to preparethe C₆₀ /PC membrane. Heating the membrane at 340° C. for 45 minutesunder nitrogen yielded brown solid. After precipitation and drying adark brown fibre (yield:97%) was obtained.

EXAMPLE 19 Preparation of C₆₀ -PVC Polymer

547.4 mg of PVC and 5.4 mg of C₆₀ were grinded thoroughly inside apestle. Transferring the mixture to a schlenk and heating at 180° C. for1 hour under nitrogen yielded brown solid. The resulting copolymer wasdissolved in 10 ml of THF, and the solution was added dropwise throughthe cotton wool to about 10 ml of hexane. A small amount of blackparticles remained on the filter paper. The precipitated polymer wasfiltered off using a Gooch crucible and dried at room temperature undervacuum for 2 days. Dark brown fibre (yield:96%) was obtained.

The observations made with respect to the samples manufactured by theabove Examples indicate UV filtering properties for the fullerenecontaining materials. Analysis of the UV spectra of further materialsmade by the above Examples confirms this. In the following UV spectrawere recorded using a Milton Roy Spectronic 3000 Diode ArraySpectrometer. For the samples in solution, the spectra were measured atroom temperature using a 1 cm square quartz cell. Either ethanol, THF orDMSO was used as reference. Membranes and glasses were measured directlyand a reference blank was used, in these cases the pathlength was thethickness of the membranes and the glasses respectively.

FIGS. 5(a) and (b) shows the optical transmission spectra of varyingconcentrations of ethanol solutions of a C₆₀ derivative, H_(x) C₆₀[NH(CH₂)₆ OH]_(x) plotted on linear and semilogarithmic scalesrespectively. While C₆₀ is virtually insoluble in lower alcohols, theaminated derivative is very soluble in ethanol and forms clear solutionsat high concentrations.

As can be seen from FIGS. 5(a) & (b) the transmission spectra at allconcentrations investigated are structureless in the manner oftransmission curves for cut-off filters. However, unlike dyed filters noUV hole is observed in the 300-400 nm region. It should also be notedthat as the concentration of the C₆₀ derivative increases thetransmission spectrum is shifted to a longer wavelength with littlechange in shape.

The cut-off wavelength (λ_(c)) may be defined as the wavelength at whichlight transmittance is 0.1%. When the concentration of the aminatedcompound is 0.009%, λ_(c) is located at 239.7 nm, which is in thebeginning of the ultraviolet region. When the concentration reaches9.165% λ_(c) shifts to 713.3 nm which is near the infra-red region. Thusvarying the concentration of the aminated compound allows the cut-offwavelength to be simply adjusted at will.

FIG. 6 shows that the cut-off wavelength also depends slightly on thesolvent. FIG. 6 plots the cut-off wavelength against concentration forsolutions of H_(x) C₆₀ [NH(CH₂)₆ OH]_(x) in ethanol, methanol andn-butanol respectively. These differences may allow the transmissionspectra of the aminated compound to be "fine-tuned". FIG. 6 also showsthat λ_(c) -c follows a semilogarithmic relation and λ_(c) increaseslinearly with log₁₀ c:

    λ.sub.c αlog.sub.10 (bc)+k

where λ_(c) =cut-off wavelength at which light transmittance is 0.1%

b=path-length of sample

c=concentration of sample

α=constant

k=constant

In addition to methanol, ethanol and n-butanol, this semilogarithmicrelationship holds for other solvents as well. The experimentallyobtained values of α and k for different solvents are summarised inTable 2:

                  TABLE 2                                                         ______________________________________                                        Solvatochromism in H.sub.x C.sub.60 [NH(CH.sub.2).sub.6 OH].sub.x.sup.a       no.        Solvent     α.sup.b                                                                        k (nm).sup.b                                    ______________________________________                                        1          o-cresol    197.5  420.8                                           2          MeOH        182.3  438.6                                           3          n-PrOH      170.5  438.9                                           4          n-BuOH      167.1  391.5                                           5          DMSO        166.6  432.9                                           6          EtOH        154.8  399.7                                           7          m-cresol    134.4  459.3                                           ______________________________________                                         .sup.a at room temperature, pathlength: 1 cm                                  .sup.b from .sub.c = αlog (bc) + k                                 

FIGS. 7(a) and (b) show the transmission spectra for ethanol solutionsof H_(x) C₆₀ [NH(CH₂)₃ Si(OEt)₃ ]_(x) and H_(x) C₆₀ (NH-cyclo-C₆ H₁₁),respectively. It will be noted that these transmission spectra are verysimilar to FIG. 5. The curves are structureless at all concentrationsand the cut-off wavelength shifts to higher values as the concentrationincreases. Furthermore λ_(c) -c plots for all C₆₀ derivatives showsimilar semilogarithmic relationships (see FIG. 8). In addition thecut-off frequencies are stable over time. FIG. 9 is a plot of cut-offwavelength against time for various solutions.

FIG. 10 shows the transmission spectra of THF solutions of poly(C₆₀-co-MMA) (C₆₀ content 0.97 wt %) measured at room temperature using a 1cm square quartz cell. The spectra are similar to those obtained for theaminated derivatives and similar results can be obtained for the otherfullerenated polymers: C₆₀ -PC, C₆₀ -PVC, and C₆₀ -PS.

FIGS. 11(a) and (b) show the concentration dependence of the cut-offwavelength for poly(C₆₀ -co-MMA) and poly(C₆₀ -co-styrene) respectively.FIGS. 11(a) and (b) show that these two polymers have the samesemilogarithmic relationship as the previously discussed aminatedderivatives. The semilogarithmic relationship also holds for C₆₀-containing polymers regardless of whether they are prepared by polymerreactions of C₆₀ with preformed polymers (FIGS. 12 and 13) or bycopolymerization with appropriate monomers (FIGS. 11(a) and (b)).

FIG. 14 shows the transmission spectra of C₆₀ -CR-39 copolymer films,and again the same patterns can be seen as before. Once again asemilogarithimic dependency is found for the cut-off frequency withreagrd to concentration (once allowance has been made for the fact thatin a membrance the thickness will be varying)--see FIG. 15. Againsimilar results are obtained with fullerene containing glasses preparedby the sol-gel manner described previously (FIGS. 16 and 17).

In summary the concentration dependence of the cut-off frequency meansthat the filtering properties of an optical material manufactured fromsuch fullerene-containing materials can be easily controlled andadjusted by altering the concentration of the fullerene component. Sincethe fullerene materials are non-toxic they may be used as UV-protectivecontact lenses and skin cosmetics (eg creams and lotions). By simplychanging the fullerene content the fullerene materials can completelyblock light in a wide spectral range while allowing high transmission ofthe light above specified wavelengths. Thus these materials may also beused in applications such as opthalmic lenses, optical filters foroptical processing and communication, shielding screens for TV and PCmonitors, sunglasses and protective goggles, containers, packagingmaterials and many others.

The above examples and embodiments are of course described by way ofexample and illustration only, since numerous modifications andvariations will be apparent to those skilled in the art withoutdeparting from the spirit and scope of the invention.

We claim:
 1. A homogeneous, transparent fullerene containing siliconglass that is suitable for use as an optical filtering material that isproduced by the reaction of tetraethylorthosilicate (TEOS) and ananimated fullerene derivative in an aqueous ethanol solution.
 2. Thehomogeneous, transparent fullerene glass of claim 1, wherein theanimated fullerene derivative that is reacted with TEOS is H_(x) C₆₀[NH(CH₂)₆ OH]_(x).
 3. The homogeneous, transparent fullerene glass ofclaim 1, wherein said animated fullerene derivative is H_(x) C₆₀[NH-cyclo-C₆ H₁₁ ]_(x).
 4. The homogeneous, transparent fullerene glassof claim 1, wherein said animated fullerene derivative is H_(x) C₆₀[NH(CH₂ CH₂ O)₂ H]_(x).
 5. The homogeneous, transparent fullerene glassof claim 1, wherein said animated fullerene derivative is H_(x) C₆₀[NH(CH₂)₃ S:(OEt)₃ ]_(x).
 6. The homogeneous, transparent fullereneglass of claim 1, wherein the fullerene content is at least about 0.55%.7. The homogeneous, transparent fullerene glass of claim 1, whichfilters light differently based on the amount of fullerene containedtherein.